This invention relates to a novel process for the production of 2,5-dichloro-3-nitrobenzoic acid. This compound is an important intermediate in the production of 2,5-dichloro-3-aminobenzoic acid, an important selective herbicide used, for example, in the control of annual broadleaf weeds and annual grasses in soybeans and other crops.
U.S. patent application Ser. No. 133,791, filed on Mar. 25, 1980 discloses a process for the production of 2,5-dichloro-3-nitrobenzoic acid by the nitration of 2,5-dichlorobenzoic acid with mixed nitric and sulfuric acids. U.S. patent application Ser. No. 325569, filed on Nov. 27, 1981, discloses a process for the production of 2,5-dichloro-3-nitrobenzoic acid by the nitration and subsequent oxidative decarboxylation of 2,5-dichloro-p-xylene by treatment with nitric acid.
The present invention involves a one-step liquid phase process for the conversion of 2,5-dichloro-3-nitro-p-xylene into 2,5-dichloro-3-nitrobenzoic acid utilizing a catalyst system comprising of a transition metal oxidation catalyst and a bromine promoter. Most preferably the transition metal oxidation catalyst comprises a cobalt catalyst and a manganese co-catalyst. An initiator or activator may also be employed if so desired.
This novel process provides the economic benefits of a one-step process coupled with the additional safety features which are present when less reactive organic acids such as acetic acid, rather than large amounts of stronger inorganic acids such as nitric acid and sulfuric acid, are employed to accomplish such oxidation and decarboxylation.